The present invention relates to a liquid level sensor-switch for electrically detecting a liquid level being lower than a specified level.
Generally, a liquid level sensor-switch of this type is used, for example, in an engine oil reservoir of a portable power generator, which detects a level lowered to and below a specified level therein.
FIG. 8 is illustrative of a typical construction of a liquid level sensor-switch which is composed of a case 81 having a guide rod 82 formed therein and incorporating a float 83 which is mounted on the guide rod with a radial clearance S and movable vertically along the guide rod and having an electrode plate 84 attached to the bottom thereof. The case 81 is provided at its inner bottom surface with a pair of terminals 85 and 86 disposed symmetrically on both sides of the guide rod. As the level of oil in the case 81 falls, the float 83 moves downward along the guide rod 82. When the level of oil in the case reaches a specified low level, the float 84 puts the electrode plate 84 in contact with the paired terminals 85 and 86 on the inner bottom surface of the case 81, thereby conducting a circuit formed between the terminals for outputting an electric signal detecting the specified level.
The problem to be solved by the present invention is such that, when driving an engine with a portable power generator placed in a state tilted together with the conventional liquid level sensor-switch, the float 83 may be biased with respect to the guide rod 82 as shown in FIG. 9 (tilted in a direction of arrangement of the terminals 85 and 86) or FIG. 10 (tilted in a direction normal to the direction of arrangement of the terminals) due to the existence of clearance S between the guide rod 82 and the float 83, resulting in variations of the liquid level detected in different tilting directions.
To prevent the biased movement of the float 83, it is desirable to reduce the clearance S between the guide rod 82 and the float 83 or a side gap between the case 81 and the float 83. However, the reduction of the clearance S and the side gap may cause inclusion of oil sludge into the clearance S and the side gap, resulting in unstable movement of the float 83. This solution may have limitations.